Problem: Complete the equation of the line through $(2,1)$ and $(5,-8)$. Use exact numbers. $y=$
Explanation: Let's find the slope: $\begin{aligned} \text{Slope}&=\dfrac{(-8)-1}{5-2} \\\\ &=\dfrac{-9}{3} \\\\ &=-3 \end{aligned}$ The equation is $y=-3x+b$ for some $b$. Let's plug the point $({2},{1})$ to find $b$ : $\begin{aligned} y&=-3 x+b \\\\ {1}&=-3({2})+b \\\\ 1&=-6+b \\\\ 7&=b \end{aligned}$ The equation is $y=-3x+7$.